Rafter help
#7
  
I would like to attach a lean-to to my existing shop.  My plan is to put a metal roof on top with 2x4 purlins every two feet to nail the metal roof too. Will 2x6 with a rafter length of 14 feet either 16 in. or 2ft on center work. Or should I use a 2x8?  Currently, my shop has 2x4 trusses set at 4 feet on center--snow load is not a problem in SC. Is there any 2x I could use that I could put them 4 feet on center?

Thank you for your help.
Herb
I'm supposed to respect my elders, but it's getting harder and harder for me to find one now.
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#8
  Re: Rafter help by Herb (I would like to atta...)
I built a 12' wide by 20' long shed using 2'x6' rafters(12/12 pitch roof) on 24" centers. That roof was exposed to the wind for 20 years with zero problems.

Installed a lap seam metal roof with screws(the kind with rubber seals) on 1" by 3" purlins. Not sure I'd want to put the rafters on 4' centers, even using 2" by 4" for purlins. And would not trust nails to hold with high wind.
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#9
  Re: Rafter help by Herb (I would like to atta...)
I suffered for height, connecting to the hipped roof eave of the shop (Didn't want to cut into the shops roof).  It was 11' 6" x 19' 9.5" for the 3' sheet roofing to have a 2.5" to 3" hang over.
Metal roofing alone is pretty light even at 26 gauge. I chose 2x6 with a 1/4 crown for all of the lumber.  3 years, heavy rains, up to 70 mph winds and no problems.  All corners have a galvanized sheet metal covering the ends to keep them protected and dry. I had to set back the end 4x4's in order for the car to easily clear the turn to get under it. With the Equinox's' rear lifted door open, I have 2" clearance- close measuring. Smirk

 Use washer screws only! Screws are pretty cheap- use more than needed- especially at the ends and sides where winds like to lift things.

I use the roofing sealant cords on all seams and have never had a leak, even with such a slightly pitched roof.


 At 14' with 2x6's, I would be starting to double up on supports and the center.

I'm sure one with more experience will add to this.




[Image: G6cjWlE.jpg]
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#10
  Re: Rafter help by Herb (I would like to atta...)
(02-19-2018, 09:43 AM)Herb Wrote: I would like to attach a lean-to to my existing shop.  My plan is to put a metal roof on top with 2x4 purlins every two feet to nail the metal roof too. Will 2x6 with a rafter length of 14 feet either 16 in. or 2ft on center work. Or should I use a 2x8?  Currently, my shop has 2x4 trusses set at 4 feet on center--snow load is not a problem in SC. Is there any 2x I could use that I could put them 4 feet on center?

Thank you for your help.

Herb, depends on the pitch, 3" pitch or close to it and I would use 2x8's. If you can do a 5 or 6" pitch or more than 2x6 will work. The only way I can think of at the moment to install the rafters at 4'-0" is to install cats the same width as your rafters at 2'-0" centers. If you go this route use 2 x 8's for rafters.
Personally I would install the rafters at 2'-0" centers and the purloins on top.

mike
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#11
  Re: Rafter help by Herb (I would like to atta...)
(02-19-2018, 09:43 AM)Herb Wrote: I would like to attach a lean-to to my existing shop.  My plan is to put a metal roof on top with 2x4 purlins every two feet to nail the metal roof too. Will 2x6 with a rafter length of 14 feet either 16 in. or 2ft on center work. Or should I use a 2x8?  Currently, my shop has 2x4 trusses set at 4 feet on center--snow load is not a problem in SC. Is there any 2x I could use that I could put them 4 feet on center?

Thank you for your help.

Thanks to all of you!!!
Herb
I'm supposed to respect my elders, but it's getting harder and harder for me to find one now.
Reply
#12
  Re: Rafter help by Herb (I would like to atta...)
(02-19-2018, 09:43 AM)Herb Wrote: I would like to attach a lean-to to my existing shop.  My plan is to put a metal roof on top with 2x4 purlins every two feet to nail the metal roof too. Will 2x6 with a rafter length of 14 feet either 16 in. or 2ft on center work. Or should I use a 2x8?  Currently, my shop has 2x4 trusses set at 4 feet on center--snow load is not a problem in SC. Is there any 2x I could use that I could put them 4 feet on center?

Thank you for your help.

Conventional metal building construction has the beams perpendicular to the metal roof at anywhere from 24" to 5' on center using 2"x2" steel tubing for the frame . Depends on the usage. For a small lean to they don't need to be very tight. When using R panel don't over build your framing. If you are using the old style wavy corrugated steel I don't know what to tell you. I never use it because it has no strength and a short lifespan compared to modern metal.
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